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Artifacts in MRI


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A short list of mri artifacts

Published in: Education

Artifacts in MRI

  1. 1. Artifacts in MRI BY Arun A Dr.Shaji’s MRI Perinthalmanna
  2. 2. Common Artifacts <ul><li>Wrap around </li></ul><ul><li>Partial volume </li></ul><ul><li>Chemical shift mis registration </li></ul><ul><li>Chemical shift edge cancellation </li></ul><ul><li>Truncation </li></ul><ul><li>Motion induced ghost </li></ul><ul><li>Zipper </li></ul><ul><li>Corduroy appearance </li></ul><ul><li>Susceptibility </li></ul><ul><li>Cross excitation </li></ul><ul><li>Sub optimal fat saturation </li></ul><ul><li>Magic angle </li></ul><ul><li>Eddy current </li></ul><ul><li>Others </li></ul>
  3. 3. WRAPAROUND <ul><li>CAUSE </li></ul><ul><li>FOV too small for body part </li></ul><ul><li>CORRECTION </li></ul><ul><li>Sample data sufficient for a larger FOV </li></ul><ul><li>Use of local coil to reduce sensitivity of tissue outside image </li></ul>APPEARANCE Body parts extends beyond one edge of image and is projected at the opposite side Show Images
  4. 4. PARTIAL VOLUME <ul><li>CAUSE </li></ul><ul><li>More than one tissue is included with in a voxel </li></ul><ul><li>Usually because of thick slices </li></ul><ul><li>CORRECTION </li></ul><ul><li>Increase spatial resolution (particularly in the slice direction ) </li></ul><ul><li>APPEARANCE </li></ul><ul><li>Edge of structure contain tissues from two adjacent slices </li></ul>Show Images
  5. 5. CHEMICAL SHIFT MISREGISTRATION <ul><li>CAUSE </li></ul><ul><li>Water and fat are misregistered relative to each other </li></ul><ul><li>CORRECTION </li></ul><ul><li>Increase sampling Bandwidth per pixel </li></ul><ul><li>APPEARANCE </li></ul><ul><li>Bright band on one slice dark band on other side of water structure surrounded fat along the frequency- encoded axis </li></ul>Show Images
  6. 6. CHEMICAL SHIFT EDGE CANCELLATION <ul><li>CAUSE </li></ul><ul><li>Water and lipid signals in a voxel at fat – water interfaces destructively </li></ul><ul><li>CORRECTION </li></ul><ul><li>Use spin echo or In phase gradient echo technique </li></ul><ul><li>Suppress lipid signal intensity </li></ul><ul><li>APPEARANCE </li></ul><ul><li>Black line at fat–water interfaces </li></ul>Show Images
  7. 7. TRUNCATION <ul><li>CAUSE </li></ul><ul><li>Abrupt ,high contrast boundaries cannot be accurately represented by Fourier Transform </li></ul><ul><li>CORRECTION </li></ul><ul><li>Increase spatial resolution </li></ul><ul><li>APPEARANCE </li></ul><ul><li>Ring –down artifact at high contrast interfaces </li></ul>Show Images
  8. 8. MOTION INDUCED GHOST <ul><li>CAUSE </li></ul><ul><li>Motion causes phases changes during signal sampling </li></ul><ul><li>Or intensity changes b/w signals Both result in phase encoding errors </li></ul><ul><li>CORRECTION </li></ul><ul><li>Average multiple signals </li></ul><ul><li>Complete image acquisition rapidly </li></ul><ul><li>Trigger acquisitions so the image anatomy is constant from view to view </li></ul><ul><li>Balance gradients to eliminate gradient moment </li></ul><ul><li>Reduce signal of moving tissue </li></ul><ul><li>APPEARANCE </li></ul><ul><li>Repetitive patterned noise that resembles the source structure </li></ul><ul><li>Repeated at regular intervals along phase encoding axis </li></ul>Show Images
  9. 9. ZIPPER <ul><li>CAUSE </li></ul><ul><li>Nondecayed transverse magnetization </li></ul><ul><li>RF feed through </li></ul><ul><li>Or extraneous noise </li></ul><ul><li>CORRECTION </li></ul><ul><li>Improve spoiling of transverse magnetization </li></ul><ul><li>Alternate polarity of excitation pulses </li></ul><ul><li>Eliminate source of noise </li></ul><ul><li>APPEARANCE </li></ul><ul><li>Band of alternative white and black dots </li></ul>Show Images
  10. 10. CORDUROY APPEARANCE <ul><li>CAUSE </li></ul><ul><li>Bad data points </li></ul><ul><li>CORRECTION </li></ul><ul><li>Increase sapling of k-space </li></ul><ul><li>APPEARANCE </li></ul><ul><li>Corduroy appearance across some images </li></ul>
  11. 11. SUSCEPTIBILITY <ul><li>CAUSE </li></ul><ul><li>Magnetic field altered by heterogeneous magnetic properties in body part </li></ul><ul><li>CORRECTION </li></ul><ul><li>Eliminate source of heterogeneous susceptibility </li></ul><ul><li>Maximize sampling bandwidth </li></ul><ul><li>Minimize TE </li></ul><ul><li>Refocus echoes </li></ul><ul><li>APPEARANCE </li></ul><ul><li>Signal loss </li></ul><ul><li>Distortion </li></ul>Show Images
  12. 12. CROSS EXITATION <ul><li>CAUSE </li></ul><ul><li>RF pulse targeted to one slice particularly excites an adjacent slice </li></ul><ul><li>CORRECTION </li></ul><ul><li>Use gap b/t slices in 2D multislice acquisitions </li></ul><ul><li>Allow sufficient time for recovery b/w radial overlapping slice acquisitions </li></ul><ul><li>APPEARANCE </li></ul><ul><li>Reduced signal intensity </li></ul>
  13. 13. SUBOPTIMAL FAT SATURATION <ul><li>CAUSE </li></ul><ul><li>Magnetic field heterogeneity causes the lipid resonance to vary within the field of view so the fat suppression RF pulse doesn't correspond to all lipid </li></ul><ul><li>CORRECTION </li></ul><ul><li>Improve magnetic field shimming </li></ul><ul><li>Improve tuning of fat suppression pulse </li></ul><ul><li>APPEARANCE </li></ul><ul><li>increased signal intensity on lipid </li></ul><ul><li>Possibly suppression of water signal </li></ul>
  14. 14. MAGIC ANGLE <ul><li>CAUSE </li></ul><ul><li>T2 of oriented fibers depends on angle relative to magnetic field </li></ul><ul><li>CORRECTION </li></ul><ul><li>Use sufficiently long TE for structure to have long signal intensity regardless of angle </li></ul><ul><li>APPEARANCE </li></ul><ul><li>variable signal intensity on of tendons and other structures </li></ul>Show Images
  15. 15. EDDY CURRENT <ul><li>CAUSE </li></ul><ul><li>Electrical currents caused by rapidly switching gradients </li></ul><ul><li>CORRECTION </li></ul><ul><li>Improve precision of gradient pulses </li></ul><ul><li>Use eddy current compensation </li></ul><ul><li>APPEARANCE </li></ul><ul><li>Reduced peripheral signal intensity </li></ul>Show Images
  16. 16. OTHERS <ul><li>In homogeneity on fat sat </li></ul><ul><li>Annefect </li></ul><ul><li>Gradient amplifier failure </li></ul><ul><li>Spike noise </li></ul><ul><li>Spatial saturation </li></ul><ul><li>Out of slice contamination </li></ul>
  17. 17. Wrap around NEXT IMAGE
  18. 18. wraparound
  19. 19. Partial volume 3 mm Partial volume 3 mm 10 mm A partial volume artifact is any artifact which is caused by the size of the image voxel.
  20. 20. Chemicals shift NEXT IMAGE
  21. 21. Chemicals shift
  22. 22. Motion NEXT IMAGE
  23. 23. Motion
  24. 24. Metal object/susceptibility NEXT IMAGE
  25. 25. Metal object/susceptibility
  26. 26. Eddy current Metal object/susceptibility
  28. 28. ZIPPER
  29. 29. Truncation NEXT IMAGE
  30. 30. Truncation Truncation
  31. 31. Magic Angle Truncation
  32. 32. In homogeneity on fat sat NEXT IMAGE Truncation
  33. 33. Annefect NEXT IMAGE
  34. 34. Gradient amplifier failure NEXT IMAGE
  35. 35. Spike noise NEXT IMAGE Annefect
  36. 36. Spike noise NEXT IMAGE Annefect
  37. 37. Spatial saturation NEXT IMAGE Annefect
  38. 38. Out of slice contamination